In Science Fiction, a concept which occurs often, is ‘A Closed Life-Support System’. But just like eventual ‘travel at half the speed of light’, a real, closed life-support system has largely remained elusive.
Back in WW2, German Submariners knew a trick to extending the life of the air in their submarines during adverse moments, of sprinkling lime powder – i.e., CaO. But the only real effect this had, was to absorb carbon dioxide out of the air mixture in the submarine, and to hold it in some form of CaCO3 . The lime powder itself did not generate any oxygen, O2, in return for scrubbing the CO2 out of the air mixture. This actually served WW2 submariners well, because until that time, the dangers of CO2 toxicity were usually greater, than the real-life dangers of hypoxia. The era only came later really, that the USA launched various high-altitude platforms, and that hypoxia started to become a common problem, to be dealt with.
CaO reacts vigorously with H2O to form Ca(OH)2 , and nothing else.
This simple fact should not be taken to mean, that WW2 submarines had no way of generating oxygen. It only means, that lime powder as such, or other strong bases, do not generate oxygen by themselves. ( :1 )
What the current International Space Station does, is to collect various forms of moisture from the habitat, and to use ample electricity from its solar collectors, to electrolyze that water into O2 and H2. At the same time, the ISS collects CO2 from the interior air, using ethanolamine, which is a liquid, weak base. And after CO2 has been absorbed by a weak base, this gives the advantage, that the salt which results only needs to be heated to modest temperatures, to re-release the CO2. But a weakness which the ISS exhibits is then to release two waste-gasses back into space: H2 and CO2. If I’m not mistaken in this statement, the ISS falls short of achieving a real, closed life-support system. The CO2 may be released into space, but doing so ‘is made up for’ with fresh carbon introduced into the cycle, in the form of food, which is transported to the ISS.
Well when I was young, I read books, according to which certain technical problems inherent in space travel would soon be solved, which were never solved. One of them was, to devise a catalyst, or some other type of reactor, to combine H2 with CO2, in a way that produces more H2O, which could then be available for electrolysis again, and which would reduce the amount of waste to some unspecified carbonaceous solid. This carbonaceous solid, could then be made up for, in food that Astronauts ate.
But the unfortunate reality which remains is, that reactions that reduce CO2 using H2 remain unharnessed today. The closest to that which we have, is the famous water-gas reactions from the 19th century, that involve some mixture of carbon monoxide ( CO ) and H2. Well unfortunately, CO has not been reduced all the way to Cs .
(Updated 10/27/2018, 15h30 … )